1. Field of the Invention
This invention relates to a device having superior dielectric strength for terminating a cord, and, more particularly, to a modular plug comprising a plurality of terminals which are supported in a plastic housing against unintended movement with only those portions of the terminals that are coated with a corrosion-resistant material being exposed and which engage conductors that are confined in the housing in such a manner that the plug has exceptionally high dielectric strength.
2. Prior Art
Modular plugs are designed to permit a customer, as well as an installer, to insert a plug into a jack and/or to remove the plug from the jack. This provides the customer with the capability of changing cords and/or connecting newly obtained telephones with existing wall terminals. Because of the ease with which telephone handsets may be connected to and disconnected from wall terminals, handsets become portable. Still further, the customer may disconnect a retractile cord, which connects a telephone handset to a base, in order to remove kinks, and then reconnect the cord.
Modular plugs for terminating telephone cords, are known and are shown for example, in U.S. Pat. Nos. 3,699,498 and 3,761,869 which issued Oct. 17, 1972 and Sept. 25, 1973, respectively, both in the names of E. C. Hardesty, C. L. Krumreich, A. E. Mulbarger, Jr. and S. W. Walden.
Modular plugs must be constructed to avoid a reduction in dielectric strength with an accompanying decrease in breakdown voltage which could lead to a loss in service. In order to meet the dielectric strength requirements between adjacent conductors and/or terminals, a plug housing has been constructed with individual ducts or cells for receiving individual ones of the cord conductors with the cells being separated from each other by partitions which extend the height of the cells. This differs from first generation modular plugs in which the conductors were disposed side-by-side, generally in contiguous relation to one another in open-topped troughs.
While the use of individual conductor-receiving cells is beneficial from the standpoint of dielectric strength, their use causes at least one problem. Terminals that are supported in the housing extend between the cells and channels which open to an outside surface of the plug to make connections between the cord and jack wires disposed in a predetermined spacing and received in the aligned channels when the plug is inserted into a jack. However, the thickness of the floor-to-ceiling partitions of the cells causes the spacing of the cells to differ from that of the jack wires. Hence, the terminals must extend between the channels, which have the same centerline spacing as the jack wires, and the cells, which have a centerline spacing different from that of the jack wires.
An alternative to a solution in which the plug connects conductors at one spacing to jack wires at a different spacing is to change the spacing of the jack wires and the spacing at which the terminals are inserted, to that of the conductors. This is not an attractive alternative since it would require modification or replacement of all the existing machinery used in the production of modular plugs and jacks and entail considerable expense.
In a viable solution for accommodating the present jack wire and terminal insertion spacing while holding the conductors at another spacing, the terminals are reoriented within the housing as the terminals are inserted. When the terminals are first inserted into the upper reaches of the housing, the terminals are at the same spacing as the jack wires. As the terminals are driven and fully seated within the housing, the terminals are shifted laterally into essentially vertical planes which are spaced apart at distances that differ from the distances at which the jack wires are spaced apart.
A further problem that manifests itself is the molding of a plug of this size with individual cells for the conductors. Minimizing the lengths of the partitions which form the individual cells would be of help in the molding of the plug by permitting the use of a more compact, stronger core pin; however, in order to avoid a reduction in dielectric strength, any reduction in length of the individual cells must be offset by other features of the plug which enhance its dielectric strength.
The dielectric strength and hence the breakdown voltage may also be reduced because of a portability feature of modular systems in which the cavities of unused modular jacks are at times exposed to corrosive atmospheres. Then, when a plug is inserted into the jack cavity, metal contact wires in the jack which have become corroded engage terminals in the plug, thereby initiating a corrosive attach upon the terminals. Corrosion of the terminals is prevented by plating the exposed portions of the terminals with a corrosion-resistant material.
Priorly, the terminals were constructed with side edges interrupted by cutouts used as pilot holes during the forming of the terminals from a continuous strip. Unfortunately, a portion of the side edges of the terminals adjacent the jack contact wires did not engage the plastic housing when the terminals were seated within the housing. Since only the cutouts of the side edge surfaces of the terminals were plated, the exposed portions adjacent the jack wires were susceptible to corrosion.
A still further problem relates to the support of the terminals within the housing so that unintended movement of the terminals is prevented. Prior art terminals relied on side edge barbs for their support, or on the previously described side edges with intermediate cutouts. The barbs were not wholly satisfactory in preventing pivotal movement of the seated terminals, while the side edges of cutout types of terminals were subject to corrosion. A plug constructed in accordance with this invention includes terminals which are supported within the housing against unintended movement with reduced exposure of non-plated surfaces of the terminals to contaminants.